Thunderstorm Electrification—A Numerical Study

The results of a numerical model of thunderstorm electrification that includes riming electrification compare favorably with many cloud observations. A strong electric charge accumulates through two major stages in the cloud: Stage 1 occurs near the cloud top (−30°C) in the developing stage when large space charges accumulate due to gravitational separation between negative graupel and positive snow crystals. Stage 2 occurs near the −10°C level in the mature stage. In stage 2 negative space charge greatly accumulates when negative graupel particles falling from upper levels of the cloud are combined with upward moving negative snow crystals from lower levels. Positive charging of graupel below the −10°C level plays a critical role in accumulation of the large negative space charge at that level. Electric development depends highly on microphysical processes, and different electric structures are calculated for maritime and continental thunderstorms. Based on model results, reasons for infrequent lightning over oceanic tropical areas are discussed.